Chromosome polymorphisms in natural populations of the South American grasshopper Sinipta dalmani

Abstract

Six populations of Sinipta dalmani from the provinces of Buenos Aires and Entre Rios (Argentina) were analyzed. The populations of "El Palmar" National Park (Entre Rios) were polymorphic for pericentric inversions in pairs M4 and M7 and for a centric fusion involving pair M5 and the X chromosome. The M4 inversion remained similar over time and the karyomorphic frequencies did not depart from those expected according to the Hardy-Weinberg equilibrium. The analysis of chiasma frequency and distribution showed clear intra-and interchromosome effects of the different chromosome rearrangements. Both inversions and centric fusions were related with total or partial crossing over restriction in heterozygous condition, leading to a genetic differentiation between rearranged and non-rearranged chromosomes. The chromosome polymorphisms analyzed herein were associated with an increase in the number of terminal chiasmata both in the rearranged chromosomes (heterozygous centric fusion and homozygous M4 inversion) and in the other chromosomes (M4 inversion). Our results showed that the chromosome polymorphisms in S. dalmani may be associated with a significant decrease in genetic recombination, which may explain in part their maintenance in some areas of its geographical distribution.

Micro-Evolution in Grasshoppers Mediated by Polymorphic Robertsonian Translocations

“…Again, the spontaneous M6-M6/M7-M7 trivalent shows an irregular meiotic behavior (77% of linear orientation) leading to 51% of aneuploid metaphase II (in the case of L. argentina, MII plates are usually not analyzable), and chiasma frequency and position remain unaffected. By contrast, the polymorphic X/M5 fusion triggers a significant reduction in the frequency of chiasmata and their displacement to terminal position (Remis 1990, 2008). …”

“…In Sinipta dalmani Stål (Acrididae: Gomphocerinae), which is widely distributed throughout Argentina and Uruguay, a polymorphism for a centric fusion between the X chromosome and an autosome was found in three populations confined to a restricted protected area in central east Argentina (Remis 1990, 2008). The centric fusion involving the sex chromosome is present in a polymorphic state (Remis 1990), a unique situation in Orthoptera, although there are several instances in which fixed X-autosome fusions allow the distinction between related Orthoptera races or species (Hewitt 1979).…”

Relationship between Chromosomal Races/Subraces in the Brachypterous Grasshopper Podisma sapporensis (Orthoptera: Acrididae) Inferred from Mitochondrial ND2 and COI Gene Sequences

“…In Sinipta dalmani Stål (Acrididae: Gomphocerinae), which is widely distributed throughout Argentina and Uruguay, a polymorphism for a centric fusion between the X chromosome and an autosome was found in three populations confined to a restricted pro-tected area in central east Argentina (Remis 1990(Remis , 2008. The centric fusion involving the sex chromosome is present in a polymorphic state (Remis 1990), a unique situation in Orthoptera, although there are several instances in which fixed X-autosome fusions allow the distinction between related Orthoptera races or species (Hewitt 1979).…”

“…The frequency of the fusion in the different samples of S. dalmani was low, and there were no statistical differences among populations or among years. This fusion was associated both with an increase in terminal chiasma frequency in the fused pair (Remis 2008) and with a decrease in the frequency of functional sperm (Remis 1993). Thus, based on the temporal stability, the influence on sperm formation, and the particular effect on genetic recombination, it is tempting to suggest a non-neutral explanation for the maintenance of this fusion at a low frequency (Remis 1993).…”

“…Again, the spontaneous M6-M6/M7-M7 trivalent shows an irregular meiotic behavior (77% of linear orientation) leading to 51% of aneuploid metaphase II (in the case of L. argentina, MII plates are usually not analyzable), and chiasma frequency and position remain unaffected. By contrast, the poly-morphic X/M5 fusion triggers a significant reduction in the frequency of chiasmata and their displacement to terminal position (Remis 1990(Remis , 2008.…”